A new report from the U.S. Census Bureau helps to fill the gap, providing detailed estimates of different types of density for America’s metros. This includes new data on “population-weighted density” as well as of density at various distances from the city center. Population-weighted density, which essentially measures the actual concentration of people within a metro, is an important improvement on the standard measure of density. For this reason, I like to think of it as a measure of concentrated density. The Census calculates population-weighted density based on the average densities of the separate census tracts that make up a metro.
The differences in the two density measures are striking. The overall density across all 366 U.S. metro areas is 283 people per square mile. Concentrated or population-weighted density for all metros is over 20 times higher, at 6,321 people per square mile.
This Census report is not the first to use population-weighted density. A 2001 study by Gary Barnes of the University of Minnesota developed such a measure to examine sprawl and commuting patterns. In 2008, Jordan Rappaport of the Kansas City Fed published an intriguing study in the Journal of Urban Economics (non-gated version here), which looked at the relationship between density (including population-weighted density) and the productivity of regions. Christopher Bradford, who blogs at his Austin Contrarian, has also advocated for using population-weighted density to better understand urban development…
New York and Los Angeles are good examples of the differences between these two density measures. While they are close in the average density — 2,826 for New York versus 2,646 for L.A. — the New York metro has much higher levels of concentrated or population-weighted density, 31,251 versus 12,114 people per square mile. San Francisco, which has lower average density than L.A. (1,755 people per square mile), tops L.A. on population-weighted density with 12,145 people per square mile.
It sounds like the new density measure uses the average densities of Census tracts which then limits the effect of sprawl as these less dense tracts, of which there are necessarily more in burgeoning metropolitan regions, are averaged out by the denser tracts. In other words, the effects of sprawl are less pronounced in this newer measure.
This reminds me of an interesting density fact: if you use the basic measure of density (total population of metro land divided by land in the metro area), the Los Angeles metro region has a higher density than New York City. But, of course, New York City is much more dense at its core while LA is more known for its sprawl.